Improvement in casting molten metal



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UNITED STATES 'Farmer Ormea JOSEPH DE ROSTHORN, OF VIENNA, AUSTRIA, ASSIGNOR TO OLEMENS I-IERSOI-IEL, OF DAVENPORT, IOIVA.

IMPROVEMENT IN CASTING MOLTEN METAL...

Specification forming part of Letters Patent No. 4559i?, dated January 17, i865.

To all whom, t 11i/ay concern.-

Be it known that l, JosnPH DE Ros'rrionn, of Vienna, in the Empire oil Austria,- have invented an Improvement in the Method of Oasting Metals 5 and I do hereby declare that the following, taken in connection with the drawings which accompany and form part of this specification, is a description of my invention sui'lcient to enable those skilled in the art to practice it.

To better show the nature and purposes of my invention, it will be well to first enter into an explanation of the present method of castinfr.

ln consequence of the diminution of Volume or shrinking of the metals or alloys used for technical purposes during their transitionfrom a melted or liquid to a solid state it has always been found necessary to add asurplus of the molten metal in order that a part at least of this surplus should enter into the body being cast, and thus make up for theloss of volume by shrinkage. The above-mentioned surplus is variously called. Herein it will be termed the riser head7 or risen This riser is intended7 however, to act in another manner also-namely, to increase the density of the casting as much as possible and to hinder-its becoming porous. It does this byitsinherent hydrostatic pressure, as long, at least, as there is any -quantity of liquid metal in it. The higher and more voluminous the riser is, therefore, the denser and compacter the casting will be, and the better defined its exterior surface. On the other hand, the cost of the casting is increased thereby very much, and a consideration of this fact sets a certain limit to the size of the riser used. If, however, as may happen in certain cases, the expense should be considered as a secondary object and the riser given an abnormal size, nevertheless that degree of density in the casting would not be had which is attained by the use of my inexpensive method, and which consists, simply, in substituting for the hydrostatic pressure oi' the liquid metal in the riser a very much greater pressure produced by mechanical means, and one acting constant and undiminished all through the period of cooling, whereas the pressure of the riser constantly diminishes and becomes almost nothing at the time it is most needed. A simple examination of the process of cooling in castings is suflicient to dispel any doubts as to the truth of this assertion. After the metal has filled the mold in a perfectly iuid condition a certain length of time, it begins to cool on the outside where it comes in contact with the cold sides of the mold, and forms a crust the thickness of which increases as the cooling process advances, while inside oi' this crust, iu the casting7 as well as in the riser, there is still liquid metal exerting hydrostatic pressure corresponding to its height, and thereby increasing the density of all parts of the column in proportion to the height thereof, and of such other parts of the casting as are not too hard and cool to be affected by the pressure. The liquidity or the inside metal diminishes, however, too fast to allow the pressure to pro duce eii'ect on the center of the casting, and it is soon of a thick semiiiuid consistency, in consequence of which its action as a hydrostatic column of pressure diminishes more and more and becomes finally a minimum, and this, too,j ust at the time when the most pressure ought to act upon the casting. Every founder or engineer knows this to be the case. In every voluminous casting the layer on the immediate outside has the greatest density, gradually diminishing in density toward the center, where it is the weakest to all tests. rIhis evil may be very nearly removed by applying an exterior mechanical pressure during the period in which the semi-fluidity ol' the metal increases, and the hydrostatic press ure exercised by the riser diminishes. I use for this purpose the weight of any body-say an iron blockwhich presses awooden plunger into the metal of a short riser until the casting has become perfectly cold.

To illustrate my invention we will take, for example, the casting of a light cannon--saya four-pounder. According to the usual method, a riser of about thirty-six inches in height would be used, whose weight may be about four hundred-weight-that is, about the weight of theinished cannondand which must be cut off when the cannon has cooled. In using my method a 'riserof about twelveinches in height is more than suflieient. To produce the nieehanical pressure a body, A, (see iigure,)

of any size and of a sufficient weight, is used.

up or downand arranged to be supported ona tripod. When themold hasbeen filled with metal, this apparatus is brought over the riser by means of a crane or windlass and fixed in such a manner that the axis of the plunger B is in line with the axis of the riser. Having brought it into this position, the tripod is brought to the support of the guide-box F, so that now B will sink vertically, even after it has been unhung from the crane or windlass. During'this time a crust has formed on the top of the riser, the formation of which may, however, be accelerated by sprinklingit with cold water. Now, the plunger Bis allowed carefully and slowly to settle, and it will break through the crust and settle a litlittle into theliquid metal beneath. In doing so a little of the liquid metal will be forced up alongside of the plunger through the cracks in the crust, while its lower surface will slowly burn to charcoal. If, now, the sinking of the weight is suspended till the abovementioned pressed-out metal has cooled, we find, singular as it may appear, th at the plunger B works, as though in a stuffing-box, through the inerusted metal, and none of the liquid metal, or none of any consequence, in the inside is pressed out upon the surface, so that the action of this plunger is similar to that of the piston of a hydraulic press. Now the rod is unfastened from the crane, and the total weight of A is allowed to act, which presses the plunger very slowly and always hermetieally tight, or practically so, through the crust into the liquid metal beneath, making thek plunger into charcoal. rlhe metal of the casting remains exposed, therefore, to the same constant pressure during the whole process ol' cooling, and attains, in consequence of this, a density and strength which no mere riser, be it ever so voluminous and high, can ever produce, because, as explained above, its action diminishes asl the metal cools. Besides this, there is still the important advantage that the pressing weight can be made as great as needed-say ten times as large as could be got in using a riser, the weight of which has narrow limits, from economical reasons.

Vhether, now, the plunger is of wood or any other material, whether the pressure on the same is produced by a dead-weight, by a screw, or any other mechanical eontrivanee, or whether, in the casting of small objects, it is produced by the immediate action of the hand ol' JOSEPH DE ROSTHORN.

fitnessesz E. HELLns LARI( I N, WM. M. Bierens. 

